On Wed, Nov 26, 2014 at 6:20 PM, Steven D'Aprano <st...@pearwood.info> wrote: > On Wed, Nov 26, 2014 at 05:23:40PM -0600, boB Stepp wrote: [...] >> First question: How can the printLabel() function see the list >> variable, l, defined outside of this function? I thought that >> functions only had access to variables local to the function and >> whatever else is passed to it during the function call. > > No, they also have access to globals and built-ins. You define the list > l at the top level of your module. That makes it a global, so the > printLavel() function can see it. > > Note that this principle is critical to Python, otherwise functions > couldn't call each other, or even built-ins! If you have two functions: > > def f(): return g() > > def g(): return "Hello!" > > "g" is a global "variable" and f() can see it, otherwise it couldn't > call it.
So any variables lower in the program are accessible to those above it? > I put variable in scare-quotes because it's actually more of a > pseudo-constant, a constant by convention, since it is very unusual to > change things you define as a function. To be more precise, the *name* > "g" which refers to the function exists in the module's global scope. As > a short-cut, we call such names "global variables", even if they never > vary. > > You only need to declare a global variable inside a function if you are > re-assigning a value to it. Hence: > > a = 1 > b = 2 > def test(): > global b > b = b + a So even though test() has access to a and b, it won't change b when called unless b is declared global inside the function? > [...] >> Third: I am always open to stylistic comments and how to be more pythonic! > > Fix your variable names! I knew I would be dinged on this, but I wanted to get my main question (about global/local) out there before I left work. The code I posted has been changed numerous times as I dickered around with Tkinter all day today. Despite having Grayson's book on Tkinter, it has been hard going for me. I PROMISE crummy variable names will not make it into the final code. Once I get the logic working and the appearance like I want it and more importantly understand what is going on, I am going to rewrite everything from scratch. > You have a variable called "buttonNumber" which holds a LIST, not a > number. Confusing! In an earlier version buttonNumber was a number. > You have another variable called "1", or is that "I", no sorry it's "l". > Notice that depending on the font you use, 1 I and l can look almost > exactly the same. That's a bad thing. Also, the name "l" doesn't mean > anything, it doesn't tell you the purpose of the variable. Originally l (ell) was a physical list written out. I am not used to the way python iterates, so I was playing around with this feature in different ways until I was sure I saw what it was doing, especially with the 2-tuples as list elements. Now that I see how this seems to work, I am planning on having a configuration file of some sort that will populate this list. Where I work we have multiple centers and people will have different versions of this list. So I intend to separate this out and each center can have their own custom radiobutton list to choose from. > Then there is another variable called "var". That's nice, we already > know it's a variable, but what role does it play in your program? Try to > find a more descriptive name. I have been switching back and forth between different python books. The name var came from Grayson's generic examples. I also got caught out by "str" as a variable name on an earlier question. That particular book is especially bad in variable names. But again, instead of renaming other people's code snippets, I tend to use them as is while I am experimenting with what their snippets are trying to do.I suppose I should be more diligent even during my "play" time in case I wind up copying and pasting portions of the play code into code I intend to keep. I imagine I might not remember to change all of the awful names into good ones. Anyway thanks for your insights! -- boB _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
